Son Doong Cave in Vietnam – which is so big it contains a jungle and a river – is now open for public tours. But don’t expect it to become crowded: just 224 tourists will be permitted to visit this year

It’s so big you could fit a 40-storey skyscraper inside, but Son Doong cave remained undiscovered until a local man found it in 1991. Even then, no one explored beyond its vast entrance until British cavers visited in 2009. All photographs: Ran Deboodt

Ropes and harness are needed to get inside Son Doong, and any visitors will need to rappel 80 metres to reach the cave floor.

Pilot tours took place in August, but so far only 10 people have visited. Oxalis Adventures have been working closely with the government to ensure a sustainable future for the cave: this year they are able to take 224 tourists to Son Doong.

The first night of the six-day tour will see visitors camp near the Hand of Dog, a giant stalagmite said to resemble a dog paw.

Inside the cave is a huge river – but the source of it remains unknown. In March, a team from the British Cave Research Association, who first explored Son Doong, will return to try and shed more light on the cave’s many mysteries.

New species of plant have been discovered by scientists within the cave’s lush interior.

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